Optical encoders use optical signals to detect mechanical positions and motions in various types of systems. The mechanical positions and motions detected by optical encoders can be related to linear or rotational displacements of moveable components, such as shafts of motors. There are two common types of optical encoders, absolute position encoders and incremental encoders. Both types of optical encoders can determine mechanical positions and motions. The absolute position encoders can determine the exact mechanical position at any moment of operation, even at power-up. The incremental encoders, on the other hand, lose the existing position data at power-down, and cannot determine the exact mechanical position at power-up. However, the incremental encoders are less expensive and require less processing power than the absolute position encoders. Thus, the incremental encoders enjoy a greater market share than the absolute position encoders.
A simple conventional optical encoder typically includes an encoder member positioned between a light source and a photodetector. The encoder member includes a number of openings, which allow light from the light source to reach the photodetector as the encoder member is rotated or linearly displaced with respect to the light source and the photodetector. The photodetector generates signals in response to incident light that can be analyzed to determine the relative position of the encoder member with respect to the light source and the photodetector.
A typical absolute position optical encoder uses an encoder member with multiple optical tracks of opaque and transparent regions to provide unique optical information at different positions along the encoder member. At each predefined position, a unique combination of transmitted light due to the opaque and transparent regions of the optical tracks is sensed at multiple photodetectors. Thus, the absolute position optical encoder can determine the relative position of the encoder member by optically sensing the light transmitted through the optical tracks on the encoder member.
A concern with conventional absolute position optical encoders is that encoder members with multiple optical tracks are relatively expensive and difficult to manufacture. In addition, more optical tracks are needed for larger or longer encoder member, which increases the complexity and manufacturing costs of the optical encoder.
In view of these concerns, there is a need for a cost-effective optical encoder.